Pope Francis has said that he would be willing to baptise aliens if they came to the Vatican, asking “who are we to close doors” to anyone - even Martians.

In a homily yesterday dedicated to the concepts of acceptance and inclusion, Francis recalled a Bible story about the conversion of the first pagans to Christianity, according to reports on Vatican Radio.

He said Catholicism was a church of “open doors”, and that it was up to Christians to accept the Holy Spirit however “unthinkable” and “unimaginable” it appeared.

Describing how, according to the Bible, Peter was criticised by the Christians of Jerusalem for making contact with a community of “unclean” pagans, Francis said that at the time that too was “unthinkable”.

“If, for example, tomorrow an expedition of Martians came to us here and one said ‘I want to be baptised!’, what would happen?”

Clarifying that he really was talking about aliens, the Pope said: “Martians, right? Green, with long noses and big ears, like in children’s drawings.”

Francis said that Christianity had struggled from its earliest stages with the temptation to reject “the living presence of God” in various forms.

But he added: “When the Lord shows us the way, who are we to say, ‘No, Lord, it is not prudent! No, let's do it this way’. Who are we to close doors?”

While Francis appears to have taken the argument to its logical extreme, this is not the first time that the Vatican has raised the prospect of baptising extra-terrestrial beings.

Speaking at the British Science Festival in 2010, one of then-Pope Benedict XVI’s astronomers said he would baptise an alien “if they asked”. While he accepted that the chances of ever getting such an opportunity were slim, Guy Consolmagno said: “Any entity – no matter how many tentacles it has – has a soul.”